Id advise highly the manufacturer, if this fails then look at talking to the MLA or a good locksmiths like fast key services http://www.fastkeys.co.uk/
Joe Hart, September 2011
Advent is a DSG Own brand and so you should try them first. www.thetechguys.co.uk
However for all the laptops that I have come across replacement keys are not available - you change the whole keyboard.